Characterization of Weak Talc Layers and Implications on Open Pit Slope Design

ABSTRACT: The Arctic polymetallic volcanogenic massive sulphide deposit in Alaska, USA is hosted within a sequence largely consisting of foliated felsic schists. These schists contain a series of shallow dipping, continuous to semi-continuous talc, talc schist and chlorite-talc schist layers. The talc layers range in thickness from thin bands 2 to 20 centimeters thick, to several meters in thickness. The talc layers form the weakest geotechnical domains, posing significant risks to the interim and final highwall stability. Delineation of domain boundaries, spatial trends and geotechnical strength parameters of the talc layers are crucial inputs to evaluate appropriate potential failure mechanisms to assess the pit slope design recommendations. This paper examines the structural geology interpretation, appropriateness of the sample selection, protection and testing procedures related to the material characterization. Analysis of the laboratory test results are discussed in the context of the material characterization, selected geotechnical design strengths, and inputs to the slope stability analyses tools available to geotechnical engineers.